1. Field of the Invention
The present invention relates to a deflection yoke used with an in-line type cathode ray tube (CRT), and particularly relates to a deflection yoke for adjusting a characteristic of a magnetic field, such as convergence or purity, by rotating a multipolar magnetic ring mounted on a cylindrical neck portion of such deflection yoke.
2. Description of the Related Art
Generally, a deflection yoke used with an in-line type CRT, has a multipolar, for example, dipole or quadrupole magnetic ring. The multipolar magnetic ring is used for adjustment of a magnetic field characteristic such as convergence or purity of a CRT by tuning a position of such the multipolar magnetic ring.
FIG. 8 is a perspective view for explaining an example of a deflection yoke for a CRT. In FIG. 8, the deflection yoke comprises a pair of separators 1a and 1b made by an insulating material, a pair of horizontal deflection coils (not shown) in inside of the deflection yoke, a pair of vertical deflection coils 7 on the outside of the deflection yoke, and a pair of cores 2 on the outer side of the vertical deflection coil 7. A flange if is formed in a narrower diameter side of the first separator 1a and the second separator 1b, and a cylindrical neck portion 103 is formed in the flange 1f. A clamp band 5 with a screw 6 is loaded on the upper portion of the neck portion 103 to stabilize deflection yoke on to CRT.
FIG. 9 is a partial perspective view for explaining the example of the deflection yoke shown in FIG. 8. In FIG. 9, the cylindrical neck portion 103 having tongues 103a through 103f, is formed on a flange 1f with the first and second separators 1a and 1b. 
The cylindrical neck portion 103 is inwardly flexible as it has slits 104a through 104f. A clamp band 5 for fixing the deflection yoke to a neck of the CRT is provided on the upper side of the neck portion 103. The screw 6 is screwed to the clamp band 5, and fastens the deflection yoke to the neck of the CRT by tightening the clamp band 5 about the neck portion 103. A prominence 14 is formed on the upper portion of tongues 103c and 103f to fit with a pair of hole 5a and 5b formed in the clamp band 5. The prominence 14 has a slope in downward direction for leading the holes 5a and 5b to make the clamp band 5 easily fit with the neck portion 103. The clamp band 5 with a screw 6 is loaded on the upper portion of the neck portion 103 to stabilize the deflection yoke on to the CRT.
A magnetic ring 10 and a magnetic ring 11 having a multipolar magnet respectively are provided between the clamp band 5 and the flange 1f of the first and second separators 1a and 1b. FIG. 9 shows the clamp band 5 and the magnetic rings 10 and 11 being removed from the neck portion 103. Generally, the magnetic rings 10 and 11 comprise material dispersed with magnetic powder such as barium ferrite or the Alnico alloy substance evenly on a nylon plastic. As the magnetic ring has variety in size at manufacturing, the inner diameter of the magnetic rings 10 and 11 is 0.4 mm wider at maximum than the outer diameter of the neck portion 103, in order to avoid the magnetic ring being tightfitting with the neck portion 103.
More precisely, protrusions 12a and 12b are provided at the bottom of the neck portion 103, and are flexible in the longitudinal direction of the neck of the CRT (i.e. the direction of a Z axis). A hook 13 having a claw 13a of triangular shape at their distal ends are formed in the tongues 103c and 103f of the neck portion 103. The magnetic rings 10 and 11 are inserted from the rear side of the deflection yoke, about the neck portion 103 between the protrusions 12a and 12b, and the claw 13a. 
FIG. 10 is a cross-sectional view of the neck portion 103 along with the direction of the Z axis. An edge side 13a1 of the claw 13a is almost orthogonal with the Z axis and a sloped side 13a2 of the claw 13a stick out with length d1 which is about 1.3 mm long enough to hold the magnetic ring being attached between the protrusions 12a and 12b, and the claw 13a. An outer side 13a3 of the claw 13a is provided to maintain the strength of metal mold for molding the separators 1a and 1b. The outer side 13a3 is almost parallel to the Z axis and has length of approximately 0.3 mm.
Recently, there has been a need for small display monitor using CRT in the market. In order to provide such a small display, the length of CRT and the deflection yoke is required to be shorter. For this reason, the distance between the bottom side of the clamp band 5 and the bottom side of magnetic rings attached to the neck portion 103 is required to be shorter, and the length of the claw 13a in the direction of Z axis is required to be 1.3 mm at maximum. Under circumstance, the length of each side of the claw 13a should be set to make slope angle xcex8 of the slope side 13a2 bigger so that the magnetic rings can be easily attached to the neck portion 103.
A slope side 13a2s is a start position of the slope for the slope side 13a2. The slope side 13a2s is not set to the position coming out of the outer diameter side of the neck portion 103 but contiguous the outer diameter portion of the neck portion 103. The slope angle xcex8, for example, is 32 degrees. The reason why the slope side 13a2s does not start from the inner diameter side of the neck portion 103 (and the reason why the claw 13a has the edge side 13a1) is because the slope angle xcex8 will be maximum at this position.
As the magnetic rings 10 and 11 are inserted to the neck portion 103 from the narrower diameter side of the deflection yoke, the magnetic rings 10 and 11 contact the prominence 14 and the neck portion 103 flex inwardly to let the magnetic rings 10 and 11 pass through the prominence 14. Then the magnetic rings 10 and 11 contact the slope side 13a2 and the tongue 13 flex inwardly. Eventually, the magnetic rings 10 and 11 are held between the protrusions 12a and 12b, and the claw 13a. The distance between the protrusions 12a and 12b, and the claw 13a is lesser than the thickness of the magnetic rings 10 and 11 so that the bounce force of the protrusion 12a and 12b holds the magnetic rings 10 and 11.
The adjustment of a characteristic of a magnetic field of CRT can be accomplished by putting a deflection yoke on the CRT and rotating the magnetic rings 10 and 11. The magnetic rings can be rotate at an appropriate torque (not too tight or not too loose) by the protrusions 12a and 12b, and the claw 13a holding the magnetic rings 10 and 11 so that the magnetic rings 10 and 11 can not easily rotate before they are being fixed with a glue after the adjustment. This torque is also caused by the bounce force of the protrusions 12a and 12b in the direction of the Z axis.
FIG. 11 is a cross-sectional view of the tongues 103f and 103c of the neck portion 103 along with the direction of the Z axis where the magnetic ring 11 is being inserted. When the magnetic rings 10 and 11 is inserted in the neck portion 103 by hands, the magnetic ring 11 will occasionally be pushed to the direction shown as an arrow A in FIG. 11 which is the direction orthogonal to the Z axis. Then the tongue 103f flexes inwardly from the position shown in a dotted line. At this position, the inner circumference side of the magnetic ring 11 contacts the edge side 13a1 of the claw 13a. 
This will cause the insertion of magnetic ring 11 to the neck portion 103 difficult. Too much strength to insert the magnetic ring 11 in the neck portion 103 at this position may break the magnetic rings 10 and 11. As explained above, the magnetic rings 10 and 11 may break in the way of inserting.
Accordingly, in consideration of the above-mentioned problem of the related art, an object of the present invention is to provide a deflection yoke of which a magnetic ring is attached to the neck portion, to control convergence by tuning such magnetic ring, and which can prevent a magnetic ring from being disengaged from a neck portion without losing smooth attachment to the neck portion.
In order to achieve the above object, the present invention provides, according to an aspect thereof, a deflection yoke apparatus including neck portion (3) in a cylindrical shape formed on a subterminal portion of a funnel shaped separator having a narrower diameter portion and a wider diameter portion, a magnetic ring (10, 11, 20 and 21) rotatably mounted on the neck portion (3), a holding portion (33a, 33b) for holding the magnetic ring from the narrower diameter portion side; and a protrusion (80a, 80b, 81) formed on the neck portion having a first slope surface (80a1, 80b1) decline to the outer direction from the narrower diameter portion side to the wider diameter portion side of the neck portion, wherein the magnetic ring contacts the first slope surface before contacting the holding portion when the magnetic ring is inserted to the neck portion from the narrower diameter portion side, and the protrusion leads the magnetic ring to the holding portion.
Other objects and further features of the present invention provides the deflection yoke as mentioned above, wherein the holding portion (33a, 33b) has a second slope surface (33a0, 33b0) decline to the outer direction from the narrower diameter portion side to the wider diameter portion side of the neck portion (3), and the first slope surface (80a1, 80b1) of the protrusion leads the magnetic ring to the second slope surface of the holding portion.
Other objects and further features of the present invention provides the deflection yoke including neck portion (3) having a cylindrical shape and formed on a subterminal portion of a funnel shaped separator with a narrower diameter portion and a wider diameter portion, first protrusion (14) formed on the neck portion, clamp band (5) having a hole to fit with the first protrusion, for being attached to and for tightening up the neck portion, magnetic ring rotatably mounted on the wider diameter portion side of the neck portion than the position of the clamp band being attached to the neck portion, holding portion (33a, 33b) for holding the magnetic ring from the narrower portion side; and second protrusion (80a, 80b, 81) having a slope surface decline to the outer direction from the narrower diameter portion side to the wider diameter portion side of the neck portion, and formed on the neck portion between the first protrusion and the holding portion, wherein the magnetic ring being inserted to the neck portion contacts the slope surface before contacting the holding portion.
A deflection yoke incorporating the principles of the present invention will be described in detail with reference to the accompanying drawings, in which the same reference numerals and symbols are used to denote like or equivalent elements used in the aforementioned prior art deflection yoke, and the detailed explanation of such elements are omitted for simplicity.